Expandable to 2-dog or 3-dog system with Add-On collars; 900 Yard (1/2 mile) Range; 16 intensity levels of Nick and Continuous stimulations adjusted from the Transmitter; Positive Vibration for a "no shock" alternative training method; Digital Technology to Maximize Power; MAXX-Range Internal Collar Antenna System; Extra mild Gentle Touch Stimulation System; Fits small to large dogs-collar adjusts from 6" to 22"; Rechargeable and Completely Waterproof Collars; Ni-MH Rechargeable battery included in Collar; Weatherproof Transmitters with No-Slip/Soft-Grip rubber coating